In a redox flow battery (RF battery) described in Patent Literature (PTL) 1, an ion exchange membrane is used as a membrane, and a nonwoven fabric composed of carbon fibers is used as a positive electrode and a negative electrode. The membrane described in PTL 1 is provided with porous sheet members on respective surfaces thereof facing the positive electrode and the negative electrode. The porous sheet members are made of a material softer than a constituent material of the positive electrode and the negative electrode.